Variable timing of intake and exhaust valves of an internal combustion engine has been shown to improve engine performance. Variable valve timing may be achieved by a cam phaser that varies the phasing of the cam shaft with respect to the phasing of the crankshaft. A variable cam timing phaser relies on an output from a cam shaft position sensor to perform closed-loop control.
In the event of degradation of the cam shaft position sensor, the engine controller may command the cam shaft to a default phasing. As a result, the engine performance may be degraded. Further, for a V-type engine, two cam shaft position sensors are typically used one for each cam shaft in the two banks. Undesirable operation may occur even if one of the cam shaft position sensors has degraded.
The inventor herein has recognized that a cam shaft position for cylinders in one bank can be estimated based on information on a cam shaft position of cylinders in another bank and engine operating conditions. In one embodiment, an internal combustion engine is provided. The internal combustion engine comprises a crankshaft; a crankshaft position sensor; a first group cylinders and a second group cylinders; a first cam shaft associated with the first group; a first cam shaft position sensor in the first group; a first variable cam timing phaser coupled to said first cam shaft; a second cam shaft associated with the second group; a second variable cam timing phaser coupled to said second cam shaft; and a controller configured to adjust the second variable cam timing phaser based on the first cam shaft position sensor and acceleration of the crankshaft correlated to the first and second cylinder groups wherein the acceleration of the crankshaft is measured by the crankshaft position sensor.
In this way, variable valve timing control of at least two cam shafts may be performed in the event of degradation of one of the cam shaft position sensors, or, if a single cam shaft position sensor is present. Thus, an engine operation strategy relying on the cam shaft position can continue without being affected by degradation of one cam shaft position sensor. Furthermore, one of two cam position sensors in the V-type engine may be eliminated for cost savings or other purposes.
In another embodiment, a method for estimating a cam shaft position of a V-type internal combustion engine is provided. The engine comprises cylinders in a first bank and a second bank, a first variable cam timing phaser in the first bank, a second variable cam timing phaser in the second bank, a crankshaft position sensor, and a first cam position sensor in the first bank. The method comprises measuring average crankshaft acceleration characteristics of the cylinders in the first bank and average crankshaft acceleration characteristics of the cylinders in the second bank using the crankshaft position sensor during a power stroke; detecting a cam phasing of the first bank using the first cam position sensor; and determining a cam phasing of the second bank based on the cam phasing of the first bank and the average acceleration characteristics of the cylinders in the first bank and the second bank.
Again, in this way, variable valve timing control of at least two cam shafts may be performed in the event of degradation of one of the cam shaft position sensors, or, if a single cam shaft position sensor is present.